An exhaust system usually comprises an exhaust line in which at least one exhaust treatment device, in particular an oxidation catalyst or a particulate filter is provided for treatment of the exhaust gases coming from the internal combustion engine.
After a lengthy shutdown, a certain amount of time is required in startup of the internal combustion engine during the so-called cold-start phase until the components arranged in the exhaust line such as the exhaust treatment device reach their operating temperature. During the cold-start phase, i.e., during the period of time in which the exhaust treatment device has not yet reached its operating temperature, output emissions are elevated because the purifying effect of the exhaust treatment device cannot be manifested until reaching the operating temperature. In particular, an exhaust treatment device designed as an oxidation catalyst will have only a greatly reduced oxidizing effect for unburned or incompletely burned hydrocarbons or none at all below its operating temperature. To be able to minimize emissions as much as possible even during the cold-start phase and thus be able to do justice to increasingly severe environmental protection requirements, it is desirable to be able to make the cold-start phase of an internal combustion engine as short as possible.
DE 10 2004 048 335 A1 describes an exhaust system for an internal combustion engine, in particular in a motor vehicle, having an exhaust line and an oxidation catalyst situated therein. Upstream from the oxidation catalyst there is a pre-oxidation unit in the exhaust line, said unit being designed and connected to a secondary fuel supply, so that it preferably completely oxidizes the secondary fuel supplied to it in conjunction with an oxidizer during a catalytic converter heating mode. In this way, the cold-start phase of the internal combustion engine should be shortened in particular.